Pannier Packing

How does a couple of shirts, pair of shorts, toothbrush and towel turn into 12kg?  Susie seems to have much less stuff than me, which doesn't say a lot for my bloke pack-lite skills.  Crisis packing review last night got it down to a little over 10kg, so that will have to do for now.  Apparently Nev Chanin toured all over the world and claimed never to have carried more than 12lbs (5.5Kg) using only a saddlebag, and cycling more than a million km during his lifetime.  5.5kg!  Unreal, but then I think too much stuff is a common problem.  Another kit review needed....